Jet Stream

By Michael Crowley, Correspondent

It’s now common knowledge that waterjet propulsion is what you want when you need to go really fast, no matter what size the vessel. The waterjet’s efficiency just doesn’t drop off the way prop-driven propulsion does once you get in the neighborhood of 30 to 35 knots. The commercial industry has been aware of this for many years, but the military, except for smaller patrol craft, had been staying pretty much on the outside when it came to larger boats.

By the turn of the century, however, a segment of the military looked at larger transports for moving troops and equipment and realized that the commercial industry had already done some of the research for them with the development of waterjet-powered high-speed ferries.

In 2001, the Navy chartered the WestPac Express , a 331′ × 87′ jet-powered catamaran built by Austal Ships , as an experimental craft for moving Marines and equipment rapidly and relatively inexpensively. The program has been so successful that the charter has been extended twice.

Also in 2001, the Army worked out a lease deal for the first of three high-speed ferries from Bollinger/Incat USA LLC at $20 million dollars a year for up to three years.

The three ferries “were leased by the military to try out the concept of using high-speed vessels. They were all Incat designs over 300 feet and could make 48 knots unloaded and 40 knots loaded,” said Joe Amyot, director of sales and service for Wärtsilä Lips .

Based in part on the use of the chartered ferries, the military continued to develop plans for more high-speed, waterjet-propelled catamarans. In 2005, the Office of Naval Research took delivery of the X-Craft , also known as the Sea Fighter , a 262′ × 72′ cat powered by MTU diesel engines and GE gas turbines driving four Kamewa waterjets.

The Navy also proceeded with the development of the waterjet-powered littoral combat ship program, with plans to build up to 60 boats. Two companies were awarded contracts and are building competing prototypes: General Dynamics , which is using Wärtsilä waterjets, and Lockheed Martin , which selected Rolls-Royce ‘s Kamewa jets.

The General Dynamics’ design is a 419′ trimaran that uses two 27,192-hp gas turbines and two 12,236-hp diesels directly coupled to four Wärtsilä waterjets. The W ärtsilä LV150 and LV160 waterjets are similar to what’s in high-speed commercial ferries, according to Amyot.

The boats will use the diesel-powered waterjets below 18 knots and both the diesel and gas turbine jets for sprint speeds over 40 knots.

Lockheed Martin’s design is a 379′ monohull, which will be powered with a pair of Rolls-Royce MT30 gas turbines and two Fairbanks Morse diesels, all connected to four Kamewa 153S2 waterjets. The four jets together can handle a little over 100,000 hp.

NEW APPLICATIONS

All this talk about big-boat waterjets with five-foot intakes doesn’t mean that manufacturers of waterjets for smaller boats aren’t finding different uses for their jets – and sometimes in unusual situations.

Ultra Dynamics Inc., Columbus, Ohio, released the UltraJet 410 in July. This fills a gap in the company’s product lineup between the 376 and 451 models. (The numbers stand for the water-intake size measured in millimeters. For the 410, that equals 16.1″.)

Sometimes a product is introduced and it takes a while before it starts to get any traction. That seems to be the case with the UltraJet 305HT. It was introduced about three years ago, “but is just now starting to hit its stride, and it is proving more popular than was expected,” said Ultra Dynamics’ Graham Scott.

The idea behind the 305HT was to offer a relatively low-speed, high-thrust unit for 28- to 35-foot boats. Cable laying would be one use, said Scott, and so would military surveillance where an array of sensors has to be towed through the water.

To get the thrust required without having to go to a larger waterjet, Ultra Dynamics took the 13.4″ pump unit out of the UltraJet 340 and put it in the 305, which normally has a 12″ intake, made a few other modifications, and emerged with the 305HT. “We have more thrust but in a package that’s the same physical size as the smaller 305,” said Scott.

North American Marine Jet ‘s HH series of waterjets has been sold for about 10 years with impeller diameters of 24″ and 38″ for maximum horsepower ranges between 750 and 1,500. They generally were installed in larger boats. One of the company’s latest products is the TJ-431HH, a Traktor Jet with a 17″ impeller and horsepower range between 200 and 450.

“It’s a combination of a high-speed jet and a Traktor Jet in one that was accomplished with a new impeller design,” said Jason Hill, president of the Benton, Ark., company.

One of the first customers for the new model was the Norwegian company Maritime Partners for a 12-liter combination rescue/workboat. The first boats with the TJ-431HH jets connected to 420-hp Yanmar diesels achieved a bollard pull of 4 tons and a 30-knot top speed.

“The customer liked the bollard pull but wanted to see if we could get more speed,” said Hill. So for six months, North American Marine Jet conducted tests on the nozzle and intake. After modifications, the jets could push the boats to 35 knots and produce 4.46 tons of bollard pull forward and two tons in reverse.

Installing the jets wasn’t easy, as the hull’s deadrise was so steep that the standard jet and engine package couldn’t be installed without the jets intersecting each other. So a twin-jet skid was designed to accommodate the sharp deadrise. The first three boats went to Africa and the second three are operating in the Gulf of Mexico.

North American Marine Jet has mounted its Traktor Jet in many different types of marine craft, but one of the most unusual has to be the Arctic Escape System used on Canada’s North Slope. These are two fiberglass, tracked vehicles manufactured by Arktos Development International in Surrey, British Columbia. Each vehicle carries 50 people and is joined by a hydraulically powered articulated arm that lets the vehicles operate at independent angles as they move across the terrain or climb out of the water onto ice.

On land or ice, cleated tracks propel the vehicles, but when they break through the ice or have to go through water, waterjets provide the power.

For the past three years, the N500 waterjet from North American Marine Jet has been used for the Arctic Escape System. “In the front vehicle, the jet is angled down so it will miss the second vehicle. That has a 360-degree steerable jet. You can also use the water off the jets as a sprinkler system to go through a fire,” said Hill.

GETTING BIGGER

Getting back to big jets, the largest waterjet from Wärtsilä takes 27,000 hp. But based on U.S. Navy research and development work, that figure may be increased by two-thirds.

Both Wärtsilä and Kamewa “are working on the development of a 36-megawatt (45,000 hp) jet,” said Wärtsilä’s Amyot. Amyot said the 45,000-hp jet would be bigger than any existing waterjet. He believes it will lead the way for high-speed transports of the future.

Another item both companies are involved with as a result of their work with the military is a reduction in the size of the jet on the transom. A boat’s transom only has so much room, so shrinking the size of the jet becomes extremely important. Rolls-Royce is working on impeller and stator redesigns, while Wärtsilä has what it calls SDLq axial geometry, SDRq which features a constant inlet duct diameter that produces more thrust and a smaller jet at the transom.

With these developments, the roles are reversed and the commercial industry will stand to benefit from what the military is working on.

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